At the rate in which India population is increasing, it is said that India will surely
replace China from its number 1 position of most densely populated country of the
world after 20-30. These will lead to high rate of consumption of most valuable
natural resource „Water‟ is resulting in augmentation of pressures on the permitted
freshwater resources.In order to conserve and meet our daily demand of water
requirement, we need to think for alternative cost effective and relatively easier
technological methods of conserving water.
Rain water harvesting is one of the best methods fulfilling those
requirements.Rainwater harvesting is the accumulation and deposition of
rainwater for reuse before it reaches the aquifer. Uses include water for garden,
water for livestock, water for irrigation, etc. In many places the water collected is
just redirected to a deep pit with percolation. The harvested water can be used
as drinking water as well as for storage and other purpose like irrigation.A
sufficient, clean drinking water supply is essential to life. Millions of people
throughout the world still do not have access to this basic necessity. After decades
of work by governments and organizations to bring potable water to the poorer
people of the world, the situation is still dire. The reasons are many and varied but
generally speaking, the poor of the world cannot afford the capital intensive and
technically complex traditional water supply systems which are widely promoted by
governments and agencies throughout the world. Rainwater harvesting (RWH) is an
option that has been adopted in many areas of the world where conventional water
supply systems have failed to meet people’s needs. It is a technique that has been
used since antiquity.
Following are the main objectives of preparing this assignment:
(i)To define water harvesting and its features.
(ii)To study the advantages and disadvantages of rainwater harvesting.
(iii)To study the effectiveness and economic efficiency of rainwater harvesting
(iv)To disscuss about the studies carried out on rainwater haresting in India
(v)To study the elements of rainwater harvesting.
(vi)To study how rainwater harvesting is practiced in India.
RAINWATER HARVESTING SYSTEMS AND ITS FEATURES
Rainwater Harvesting is a simple technique of catching and holding rainwater
where its falls. Either, we can store it in tanks or we can use it to recharge
groundwater depending upon the situation.
Features of Rainwater Harvesting are:
1. Reduces urban flooding.
2. Ease in constructing system in less time.
3. Economically cheaper in construction compared to other sources, i.e. dams,
4. Rainwater harvesting is the ideal situation for those areas where there is
inadequate groundwater supply or surface resources.
5. Helps in utilizing the primary source of water and prevent the runoff from
going into sewer or storm drains, thereby reducing the load on treatment
6. Recharging water into the aquifers which help in improving the quality of
existing groundwater through dilution.
Benefits of rainwater harvesting:
Rainwater harvesting in urban and rural areas offers several benefits including
provision of supplemental water, increasing soil moisture levels for urban greenery,
increasing the groundwater table via artificial recharge, mitigating urban flooding
and improving the quality of groundwater. In homes and buildings, collected
rainwater can be used for irrigation, toilet flushing and laundry. With proper
filtration and treatment, harvested rainwater can also be used for showering,
bathing, or drinking.
The major benefits of rainwater harvesting are summarized below:
• Rainwater is a relatively clean and free source of water
• Rainwater harvesting provides a source of water at the point where it is needed
• It is owner-operated and managed
• It is socially acceptable and environmentally responsible
• It promotes self-sufficiency and conserves water resources
• Rainwater is friendly to landscape plants and gardens
• It reduces storm water runoff and non-point source pollution
Disadvantages of Rainwater Harvesting:
High Initial investment Costs - The main cost of a rainwater collection system
generally occurs during the initial construction phase and no benefit is derived until
the system is completed.
2. Regular Maintenance - Regular maintenance, cleaning and repair will be
required for the operation of a successful rainwater collection system.
3. Vulnerable Water Quality - The quality of rainwater can be affected by air
pollution, insects, and dirt or organic matter. The type and kind of construction
materials used can also adversely affect water quality.
4. Water Supply is Climate Dependent - Droughts or long periods of time with
little or no rain can cause serious problems with your supply of water.
5. Storage Capacity Limits Supply - The supply of water from a rainwater
collection system is not only limited by the amount of rainfall but also by the size of
the collection area and your storage facilities.
Effectiveness of technology
The feasibility of rainwater harvesting in a particular locality is highly dependent on the amount
and intensity of rainfall. As rainfall is usually unevenly distributed throughout the year,
rainwater harvesting can usually only serve as a supplementary source of household water. The
viability of rainwater harvesting systems is also a function of the quantity and quality of water
available from other sources, household size, per capita water requirements and available
Accounts of serious illness linked to rainwater supplies are few, suggesting that rainwater
harvesting technologies are effective sources of water supply. It would appear that the potential
for slight contamination of roof runoff from occasional bird droppings does not represent a
major health risk. Nevertheless, placing taps at about 10 cm above the base of the rainwater
storage tanks allows any debris entering the tank to settle on the bottom, where it will not affect
the quality of the stored water, provided it remains undisturbed.
Finally, effective water harvesting schemes require community participation which is enhanced
• Sensitivity to people’s needs
• Indigenous knowledge and local expertise
• Full participation and consideration of gender issues, and
• Taking consideration of prevailing farming systems as well as national policies and
Valid data on the economic efficiency of rainwater harvesting systems is not possible.
Dependent on the regional conditions (water and wastewater prices, available subsidies), the
amortization period may vary between 10 and 20 years. However, it should be taken into
consideration that for the major investment (storage and pipe work) a period of use of several
decades is expected.
The associated costs of a rainwater harvesting system are for installation, operation and
maintenance. Of the costs for installation, the storage tank represents the largest investment
which can vary between 30 and 45% of the total cost of the system dependent on system size. A
pump, a pressure controller and fittings in addition to plumber’s labor represent other major
costs of the investment.
Rainwater quality standards
The quality of rainwater used for domestic supply is of vital importance because, in most
cases, it is used for drinking. Rainwater does not always meet drinking water standards
especially with respect to bacteriological water quality.
Compared with most unprotected traditional water resources, drinking rainwater from
well-maintained roof catchments is usually safe, even if it is untreated. The official policy of the
Australian Government towards the question “Is rainwater safe to drink?” is as follows:
“Providing the rainwater is clear, has little taste or smell and is from a well-maintained system,
it is probably safe and unlikely to cause any illness for most users”. For immune-compromised
persons, however, it is recommended that rainwater is disinfected through boiling prior to
Rainwater harvesting systems can be installed in both new and existing buildings and
harvested rainwater used for different applications that do not require drinking water quality
such as toilet flushing, garden watering, irrigation, cleaning and laundry washing. Harvested
rainwater is also used in many parts of the world as a drinking water source. As rainwater is
very soft there is also less consumption of washing and cleaning powder. With rainwater
harvesting, the savings in potable water could amount up to 50% of the total household
Criteria for selection of rainwater harvesting technologies
Several factors should be considered when selecting rainwater harvesting systems for
• Type and size of catchment area
• Local rainfall data and weather patterns
• Family size
• Length of the drought period
• Alternative water sources
• Cost of the rainwater harvesting system.
When rainwater harvesting is mainly considered for irrigation, several factors should be taken
into consideration. These include:
• Rainfall amounts, intensities, and evapo-transpiration rates
• Soil infiltration rate, water holding capacity, fertility and depth of soil
• Crop characteristics such as water requirement and length of growing period
. Components of a rooftop rainwater harvesting system
Although rainwater can be harvested from many surfaces, rooftop harvesting systems are most
commonly used as the quality of harvested rainwater is usually clean following proper
installation and maintenance. The effective roof area and the material used in constructing the
roof largely influence the efficiency of collection and the water quality.
STUDIES CARRIED OUT GLOBALLY-
Today due to rising population &economical growth rate, demands for the surface water is
increasing exponentially. Rainwater harvesting is seems to be a perfect replacement for surface
& ground water as later is concerned with the rising cost as well as ecological problems.
Thus, rainwater harvesting is a cost effective and relatively lesser complex way of managing
our limited resources ensuring sustained long-term supply of water to the community. In order
to fight with the water scarcity, many countries started harvesting rain. Major players are
Germany (Biggest harvesting system in Germany is at Frankfurt Airport, collecting water from
roofs of the new terminal which has an large catchment area of 26,800 m2), Singapore (as
average annual rainfall of Singapore is 2400 mm, which is very high and best suited for
rainwater harvesting application), Tokyo (as RWH system reserves water which can be utilized
for emergency water demands for seismic disaster), etc.
STUDIES CARRIED OUT IN INDIA
Today, only 2.5 per cent of the entire world’s water is fresh, which is fit for human
consumption, agriculture and industry. In several parts of the world, however, water is being
used at a much faster rate than can be refilled by rainfall. In 2025, the per capita water
availability in India will be reduced to 1500 cubic meters from 5000 in 1950. The United
Nations warns that this shortage of freshwater could be the most serious obstacle to producing
enough food for a growing world population, reducing poverty and protecting the environment.
Hence the water scarcity is going to be a critical problem if it is not treated now in its peanut
Elements of Rainwater Harvesting
Rainwater harvesting systems generally consist of four basic elements:
(1) Collection (catchment)
(2) Conveyance system
consisting of pipes and
(3) Storage facility, and
(4) Delivery system consisting
tap or pump.
Rainwater Harvesting Practice In India
At the rate in which India’s population is increasing,Rainwater Harvesting is the
need of the hour.
In the state of Tamil Nadu, rainwater harvesting was made compulsory for every
building to avoid ground water depletion. It proved excellent results within five
years, and every other state took it as role model. Since its
implementation, Chennai saw a 50 percent rise in water level in five years and the
water quality significantly improved.
In Rajasthan, rainwater harvesting has traditionally been practiced by the people of
the Thar Desert. There are many ancient water harvesting systems in Rajasthan,
which have now been revived.
At present, in Pune (in Maharashtra), rainwater harvesting is compulsory for any
new society to be registered.
An attempt has been made at Dept. of Chemical Engineering, IISc, Bangalore to
harvest rainwater using upper surface of a solar still, which was used for water
There are good opportunities for Rainwater harvestinginKerala because Kerala is
located in a geographical area with two rainy seasons. Kerala faces severe water
scarcity between February and mid May every year. During summer, there are
drinking water shortages. During this period drinking water and other water
purposes become unavailable.
Rain water harvesting has gained popularity in Kerala through various projects
implemented by different agencies. The Rain Water Harvesting Campaign of the
Government and publicity by various media are responsible for popularizing rain
water harvesting in the state. Rainwater harvesting is viewed as a water security
measure for the State of Kerala, with two broad types of programmes.
The effectiveness of rainwater harvesting system lies in its ability to meet the
site requirements and end use preferences. Though simple, these systems are
site specific and need to be detailed out before implementation. With decrease
in availability of water, rain water harvesting presents the best option for times
Rainwater harvesting, http://en.wikipedia.org/wiki/Rainwater_harvesting .
APROJECT REPORT ON “Rain water harvesting”,http://www.slideshare.net/shalu786/rainwater-harvesting-
ASeminar ReportOn“SURVEY & ANALYSIS FOR RAINWATER HARVESTING & POSSIBLE REUSE OF WATER”,
Rainwater Harvesting in Kerala, http://en.wikipedia.org/wiki/Rainwater_harvesting_in_Kerala .
Contributed by: Tousif Raja